Suction system and process for coating arrangements avoiding the transmission of pressure differences to the coating operation

ABSTRACT

A PHOTOGRAPHIC WEB IS COATED WITH A PHOTOGRAPHIC EMULSION UNDER A ROLLER AND THE FINAL THICKNESS OF THE COATING IS EFFECTED BY AN AIR STREAM BLOWN TANGENTIALLY OVER THE COATING INTO A VACUUM CHAMBER. FLUCTUATIONS IN THE AIR STREAM ARE PREVENTED BY SUBJECTING THE AIR DISCHARGED FROM THE VACUUM CHAMBER TO A SUDDEN RESTRICTION IN ITS CROSS SECTIONAL AREA BY PASSING IT THROUGH AN APERTURED DIAPHRAGM. THIS ABRUPTLY CHANGES ITS PRESSURE IN THE RATIO OF AT LEAST 2:1 AND OBTAINS RELATIVELY HIGH AIR VELOCITY IN THE APERTURE IN THE SONIC REGION.

Sept. 12, 1972 P. HERsHoFF HAL 3,690,917

SUCTION SYSTEM AND PROCESS FOR COATING ARRANGEMENTS AVOIDING` THETRANSMISSION OF PRESSURE DIFFERENCES TO THE COATING OPERATION Filed Feb.5, 1970 INVENTOR:

PETER HEHZHOFF, HANS GEEF, WILLI SCHWENGER, WOLFGANG SCHWECHER, KURTBhO'v'VA'l"ZKI, STEPHAN PLATZ, GNTHER KOEPE,

""'f MAUS, WlLLI WALiSEh.

United States Patent O U.S. Cl. 117-34 2 Claims ABSTRACT OF THEDISCLOSURE A photographic web is coated with a photographic emulsionunder a roller and the inal thickness of the coating is eiected by anair stream blown tangentially over the coating into a vacuum chamber.Pluctuations in the air stream are prevented by subjecting the airstream discharged from the vacuum chamber to a sudden restriction in itscross sectional area by passing it through an apertured diaphragm. Thisabruptly changes its pressure in the ratio of at least 2:1 and obtainsrelatively high air velocity in the aperture in the sonic region.

This invention relates to a method and a suction system for coatingarrangements, for avoiding the transmission of pressure differences inthe suction system to the coating operation. The invention isparticularly applicable when coating webs, more especially withphotographic emulsions, the web being initially coated in a wedge-likegap and the tinal coating eiected by means of an oppositely directed airstream substantially tangential to the coating direction, said airstream blowing through a gap-forming straight edge into a vacuumchamber, from which chamber the air is drawn oif by suction.

With coating arrangements of known design, it has been found thatfluctuations in pressure in the suction system have a disadvantageouseffect on the coating operation, since the speed of the tangentialblowing air stream also iluctuates in synchronism with the pressurefluctuations, and leads to a non-uniform coating, which is shown in theform of uetuations in thickness, so-called transverse streaks.

It has now been found that these disturbing pressures are avoided by theblowing air extracted from the vacuum chamber being guided by anapertured diaphragm before entering the suction arrangement, a criticalpressure increase in the ratio of at least 2:1 being thus produced.

The result thereby achieved is that sonic speed obtains in the diaphragmaperture and all pressure waves which emanate from exciting devicesbehind the diaphragm are taken up in the diaphragm aperture, so that theactual coating position remains free from pressure uctuations and auniform coating is guaranteed.

According to the invention, in the suction extraction system of coatingarrangements for carrying out the method, an adjustable diaphragm isarranged in the air suction pipe.

The essential feature of the invention is now to be explained byreference to an example shown in the drawing.

A web 1 to be coated is moved in the direction of the arrow over aroller 2. The emulsion is supplied through supply pipe 3 and distributorsystem 4. A component stream discharges again over the rear overflowedge 5 and the pipe 6. The other part is preformed into a layer in apreproportioning wedge 7, but this layer is thicker than the layerfinally to be formed. The nished layer or coating is formed at a gap 8between the web 1 and the so-called casting straight edge 9 by thestripping action of the blowing air flowing tangentially to the web 1into the vacuum chamber 10, 12. The air is deiiected immediately afterthe straight edge 9 and is drawn by suction through the constriction 11into the chamber 12 through the connecting pipe 13, the sudden pressurechange being produced in the opening of diaphragm 14. The emulsion whichis blown off discharges through the pipe 15.

We claim:

1. A method of applying a .photographic emulsion coating to webs whichavoids the transmission of pressure fluctuations in the suction systemof coating arrangements, comprising the steps of coating the web under aroller with an excess of coating and effecting the iinal coating bymeans of an air stream directed substantially tangentially and counterto the roller coating direction, blowing the air stream over agap-forming straight edge into a vacuum chamber, from which chamber theair is extracted by a suction device, wherein before entering thesuction device, subjecting the blowing air extracted by the vacuumchamber to a sudden restriction in its cross-sectional ow area whilebeing discharged from said vacuum chamber causing a pressure change insaid discharged air in the ratio of at least 2:1 whereby its velocity isincreased to approximately sonic speed and whereby pressure iiuctuationsin the air stream are prevented and smooth uniform coating is effectedupon said web.

2. A method as set forth in claim 1 wherein said restriction is abruptlyobtained.

References Cited UNITED STATES PATENTS 3,348,964 10/ 1967 Good 118-502,681,294 6/ 1954 Beguin 117-34 3,227,136 1/ 1966 Bartlett et al. 118-632,952,559 9/ 1960 Nadeau 117-34 3,503,370 3/ 1970 Ishwata 117-343,502,494 3/1970 Ishiwata 117-34 WILLIAM D. MARTIN, Primary Examiner W.R. TRENOR, Assistant Examiner U.S. Cl. X.R. 117-61, 111, 119; 118-7, 50,63, 410

-PO-OSO UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,3,690. 917 Dated September l2, 1972 Inventoms) Peter Herzhoff et al Itiscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

[ On the cover page, in the heading, change l HERSHOFF ET AL" tOHERZHOFF ET AL Signed and Sealed this 13th day of February 1973 (SEAL)Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

